Aquaporins (AQPs) are membrane water channels expressed in many mammalian tissues that carry out fluid transport. In the eye, the specific localization of three members of the aquaporin family suggests a role in intraocular pressure regulation and corneal transparency. Immunocytochemistry has shown expression of AQP1 and AQP4 in non-pigmented ciliary epithelium, AQP1 in canal of Schlemm, AQP1 in corneal endothelium and AQP5 in corneal epithelium. To test the central hypothesis that aquaporins play a role in these functions, measurements will be done in transgenic mice lacking each of the major eye aquaporins, AQP1, AQP4 and AQP5. These knockout mice have been developed and characterized in our lab, and have been extremely useful in defining the role of aquaporins in renal, lung, brain and gastrointestinal physiology. Aim 1 will compare intraocular pressure, aqueous fluid production and outflow, and aqueous fluid compartment volume and compliance in wildtype mice and mice lacking AQP1 and AQP4, individually and together. Aim 2 will compare corneal thickness, transparency and water permeability in wildtype mice and mice lacking AQP1 and AQP5, under baseline conditions and in experimental models of corneal edema. Aim 3 utilizes a novel screening procedure to develop aquaporin inhibitors as a research tool to investigate the role of aquaporins in eye physiology, and ultimately, for the potential therapy of elevated intraocular pressure. Many of the measurements involve technically challenging innovations, the feasibility of which is demonstrated in preliminary data. The proposed research should provide clear-cut, definitive data on the role of aquaporins in eye function. If aquaporins are proven to be important, as anticipated, then modulation of aquaporin expression and/or function might provide a new therapeutic strategy for treatment of glaucoma and corneal edema.